Apparatus for measuring interstitial water content of well cores



Sept. 30, 195-2 E ANGQNA 2,612,036

APPARATUS FOR MEASURING INTERSTITIAL WATER CONTENT OF WELL CORES FiledNov. 1, 1947 a1 I as 5 Frank A. Angona INVENTOR. @M @W .AGEM

Patented Sept. 30, 1952 UNiTED STATES APPARATUS FOR MEASURING INTERSTI-TIAL WATER CONTENT OF WELL CORES Frank A. Angona, Dallas, Tern,assignor, by mesne assignments, to Socony-Vacuum Oil Company,Incorporated, New York, N. Y., a corporation of New York ApplicationNovember 1, 1947, Serial No. 783,508

4 Claims. 1

This invention relates to semi-permeable membranes and relates moreparticularly to semipermeable membranes for use in measuring theinterstitial water content of porous materials of terrestrial origin,particularly samples of cores taken from underground formationsencountered in the drilling of wells for petroleum.

It is customary in the drilling of wells for petroleum to remove samplesor cores from the various formations encountered and to test the coresfor various physical characteristics and properties. One of thecharacteristics of the cores usually determined is the interstitial, oras it is sometimes termed, the connate, water content of the cores. Inorder to minimize errors which may be encountered as a result ofevaporation of water from the cores or as a result of water entering thecore from the drilling fluid or mud employed during the drilling or" thewell, it has been proposed to determine the interstitial water contentof the cores by a method known as the restored state method. Inaccordance with this method, the cores are subjected to conditionssimulating those under which they existed in their original terrestrialpositions and their water contents measured when at equilibrium underthese conditions. In practicing this method, the core is maintained incontact with a body of free water and a pressure of a water immisciblegas or liquid imposed upon the core. The value of this pressure is suchthat the difference in pressure between the core and the body of freewater approximates the pressure diiierential between the interstitialwater of the core when in its original position in the earth and thewater table underlying the core, and this pressure differential ismaintained until the water content of the core reaches equilibrium. Thismethod is also employed ,for determining the minimum interstitial watercontent of the core, i. e., the water content which remainssubstantially constant with increase in the pressure difierential.

In order to prevent flow of the pressure inducing medium into the bodyof free water and thereby to maintain the pressure differential betweenthe core and the body of free water, a semi-permeable membrane saturatedwith water is interposed between the core and the body of free water. bedefinedas a membrane which, when saturated with one fluid, has a minimumdisplacement pressure to another fluid immiscible with the first. Statedotherwise, the membrane, when saturated with a fluid such as, forexample, water, will I":

This semi-permeable membrane may be permeable to the flow of water butwill be impermeable to the flow of another fluid, such as a gas orliquid, immiscible with the-water, until a certain minimum pressure ofthis other fluid has been exceeded. Thus, by interposing thesemi-permeable membrane between the core and the body of free water, thefluid imposing a pressure on the core will be unable to permeate throughthe membrane into the body of free water and thereby the pressuredifferential can be maintained. Further, water will be able to iiow toor from the core and the body of free water through the membrane untilthe water content of the core reaches equilibrium under the pressuredifferential imposed. v

Various types of materials have been employed for the semi-permeablemembrane. For example, consolidated materials such as unglazed porcelainor fire clay or unconsolidated materials such as barium sulfate havebeen employed. However, the use of these materials have been attendedwith certain difiiculties. Consolidated materials have low minimumdisplacement pressures. Unglazed porcelain for example, when saturatedto water, will be permeable to air or nitrogen at pressures of about 15pounds per square inch gage. Membranes made from unconsolidatedmaterials are not easily handled, and are readily disturbed or broken byrepeated removal and contacting of the core where the attainmentof'equilibrium water content is determined by weighing the core.Further, where liquids are employed for imposing a pressure on the core,membranes made from unconsolidated materials tend to be disturbed orbroken by the buoyancy effect of the liquid. 1

It is an object of this invention to providea semi-permeable membrane.It is another object of this invention to provide a semi-per" meablemembrane having a high displacement pressure. It is another object ofthis invention to make possible the measurement of interstitial water athigh pressure differentials. These and other objects of the inventionwill become apparent from the following description thereof.

The semi-permeable membrane of the inve tion consists essentially of alayer of unconsolidated material positioned between two layers ofconsolidated material. In the preferred form of the semi-permeablemembrane, the two layers of consolidated material and the layer ofunconsolidated material are maintained in contact by supporting means inorder that the membrane be readily handled without the layers comingapart.

As consolidated material, any type of porous material heretoforeemployed for semi-permeable membranes may be employed. The essentialcharacteristics of such materials are that they be porous and, whensaturated with one fluid, have a minimum displacement pressure toanother fiuid immiscible with the first. Suitable types of materials areunglazed porcelain, fire clay, ultra-fine fritted glass, pumicestone,etc.

As unconsolidated material, any type of material of small particle sizemay beemployed provided such material is not water soluble. .It ispreferable also that the material be substantially non-swelling in thepresence of water. Suitable types of material are barium sulfate,powdered silica, and powdered pumice. Preferably, however, tale isemployed.

The semi-permeable membrane of the invention has'a high displacementpressure. Thedisplacement'pressures vary'with the type of-liquidemployed for saturating the membrane, whether plain water or salinesolution, and with thefiuid employed for imposing the pressuredifierential.

The displacement pressures also vary with the type and particlesize ofthe unconsolidated materialand with the type of consolidated material.In any case, however, the displacement pressure will be considerablyhigher than the displacement pressure of the unconsolidated material orthe consolidated material alone. For example, where unglazed porcelainand talc, the tale having a particle size between 0.18 and 455 microns,are employed and the membrane is saturated with water, the displacementpressure lto airor nitrogen will beabout 40 pounds per square inch gage.

In the copending application of Paul P. Reichertz, Serial No. 766,566,filed August 6, l947,'now Patent No. 2,539,355, issued January 23, 1951,there is disclosed and claimed a method and apparatus for measuring,among other characteristics, the interstitial water content of cores.The semi-permeable membrane of the present inven tion is highly usefulwhen employed in the appa ratus of the copending application. Thefollowing more detailed description of the semhpermeable membrane of thepresent invention will be given in connection with'its use-inthe'apparatus of the copending application.

Fig. l is a sectional view of apparatus containing the semi-permeablemembrane for measurement of interstitial water of well cores.

Fig. 2 is a sectional view of a plug member containing thesemi-permeable membrane.

Fig. 3 is a plan view of the top of the plug member of Fig.2.

Figgaisa plan view of thebottom'of the'plug member of Fig. 2.

Referring now'to Fig. 1; acylindrical well'core 10, covered along itsouter edges with a coating l l of animpervious material, suchasformaldehyde phenol resin (Bakelite) methylmethacrylate resin (Lucite),or polystyrene, is positioned between a lower annular base member 12 andan upper annular base member 14. Positioned in the .upper base member l4and adjacent to the upper surface of the core!!! is a plug member 15.Maintaining the base members (2 and I4 and the plug member I5 in spacedrelationship is a rigid U-shaped strap l5. Base member i2 is held on thestrap by means of wing bolts I! and I9 and base member (4 is held on thestrap by means of screws and 2|. Tightening screws 22 and 24 hold plugmember l5 on the strap and also serve the function of tightening theplug member into close contact with the upper surface of the core H3.

Leading through the base member 12 is channel 25 connecting throughfitting 25 to pipe 21. Leading through plugmember i5 is channel 29through which pipe 30 is fitted. Pressure chamber 3| and pressureindicator 32 are connected to pipe 21 and measuring burette 34,preferably positioned levelwith the top of core i0, is connected to pipe38. Toprovide the same pressure at both the bottom and top of core I0,pipe 35 leads from 'fitting'Z'B to fitting 35 connecting with channel3-? in upper base'member 14. To prevent leakage, gasket .38 is providedin base member l2, gaskets '39 and ii) are provided in base member I 4,and gasket il .is provided in plug member I5.

Plug member l5 contains semi-permeable membrane 42. The membrane is openat its upper surface to channel 29 and pipe 30, and s adjacent at itslower surface to the exposed top of core 16. To provide a closecapillary contact :of the lower surface of the semi-permeablemembrane-with the exposed surface of the core ID, a thin sheet of'porousmaterial 44, which may be closely woven cloth or tissue paper, is placedbetween the core andmembrane. In Fig. 1, the core, the sheet of porousmaterial Mi, and the plug member l 5 are shown as being slightlyseparated. However, this separation is only for purposes of clarity inillustration. In operation, as mentioned hereinafter, the core IS, thesheet of porous material, and the plug member 15 are maintained in.close contact by means of tighteningscrews'ZZand 24.

.To determine interstitial water content of a well core, the-core isfirst leached with acetone, benzene, toluene or other suitable solventto remove oil or other liquid material naturally contained therein andthen dried of solvent. The core is next covere'dal'ong its outer edgeswith an impervious coating of methyl methacrylate resin (Lucite),formaldehyde phenol resin (Bakelite), or polystyrene and weighed.Following this, the core is completely saturated with water or with anaqueous solutionhaving the same physical or chemicalproperties of theliquid containedin the core in its original terrestrial position. Thecoreis again weighed. From the differencein 'weights,'the total porevolume of the core may be calculated knowing the density of the water orsolution. The semi-permeable membrane is also saturated with the sameliquid employed for saturating the core.

The core is positioned as shown in Fig. l and the pipe 30 isv filledfrom the top of the membrane to at least the zercimark on the measuringburette with the'same liquid employed for saturating the core. -Thedesired pressure, which may be that era 'gas 'such as air or nitrogen ora liquid im'mis'cible with th liquid employed for saturating the core,is then impressed on the core from pressure chamber 3| as measured bypressure indicator 32. Immediately after impos'ition'of'the pressure,the plug member 15 is tightened downw'ardly by means of tighteningscrews 2'2'a'nd '24 to effect a close capillary contact betweenthemembrane 42, the porous sheet M, and the exposed surface of the core I5.Upon imposing the pressure and tightening the plug member, there is aninitial rapid flow of excess liquid-'to'themeasuring burette 34 and,when this initial rapid flow of excess liquid stops, 9. reading on theburette 34 is made.

As a result of capillary forces induced by the pressure, liquid isremoved from the core and passes through the membrane 42 to the pipe 30and the burette 34. This pressure is maintained until the liquid contentof the core under the pressure imposed comes to equilibrium. Attainmentof equilibrium is a slow process and may require a period of time aslong as thirty days. When equilibrium is attained, a second reading ismade on the burette and the difference between the two readings will bethe volume of liquid removed from the core. The interstitial watercontent of the core at the pressure employed will be the difference inthe volume of liquid in the core at saturation and the volume of liquidremoved and may be expressed as the percentage of total pore volumeoccupied by the liquid.

Figs. 2, 3, and 4 illustrate the plug member I5 and the semi-permeablemembrane 42 in greater detail. The plug member 15 consists of a bodyportion 45 containing channel 29 provided with recess 46 for gasket 4|.Fitted into the body portion are threaded bushings 41 and 49 adapted toreceive tightening screws 22 and 24. Preferably, the body portion is aplastic material such as methyl methacrylate resin (Lucite),formaldehyde phenal resin (Bakelite), or polystyrene. Fitted into thebody portion is the semi-permeable membrane comprising a layer ofconsolidated material 50, a layer of unconsolidated material 51, andanother layer of consolidated material 52.

To fabricate the semi-permeable membrane, a suitably sized cylinder ofplastic material, such as methyl methacrylate resin, is made as, forexample, in a mold press. A hole having the same diameter as themembrane to be fitted is then drilled into the cylinder to form anannulus. The annulus is returned to the mold press, one end of theannulus being positioned flush with a smooth plane surface of the press.The disc of consolidated material 52 is fitted into the annulus and thelayer of unconsolidated material 5| placed on top of the disc ofconsolidated material. The layer of unconsolidated material is packedtightly in position and the disc of consolidated material 50 placed overthe layer of unconsolidated material. The remaining portion of theannulus is filled with methyl methacrylate powder and the mold pressclosed. The pressure in the mold is brought to 200 pounds per squareinch and the temperature is increased gradually to 275 F. When thistemperature is attained, the pressure is increased to 5000 pounds persquare inch, following which the mold is permitted to cool to roomtemperature. The cooled cylinder is removed from the mold and thechannel 29 is drilled therein. The recess 46 is then machined in thechannel and the gasket 41 fitted into position. Finally, holes aredrilled to accommodate the threaded bushings 41 and 49 and the bushingsfitted therein.

While I have thus described my invention, it is to be understood thatsuch description has been given by way of illustration and example only,and not by way of limitation, reference for the latter purpose being hadto the appended claims.

I claim:

1. In an apparatus for determining interstitial water content of a wellcore sample by the re tored state method, said apparatus having achamber for holding said well core sample,

means for supporting a semi-permeable membrane in contact with said wellcore sample, means for imposing upon said well core sample a pressure ofa non-aqueous fluid, and means providing a conduit leading to saidsemi-permeable membrane for passage of fluid, a semipermeable membranecomprising two unitary disks of unglazed porcelain and a layer ofpowdered talc position-ed between and in contact with said disks ofunglazed porcelain.

2. In an apparatus for determining interstitial water content of a wellcore sample by the restored state method, said apparatus having achamber for holding said well core sample, means for supporting asemi-permeable membrane in contact with said well core sample, means forimposing upon said well core sample a pressure of a non-aqueous fluid,and means providing a conduit leading to said semi-permeable membranefor passage of fluid, a semipermeable membrane comprising two unitarydisks of unglazed porcelain and a layer of powdered talc of particlesize between 0.18 and 4.5

microns positioned between and in contact with said disks of unglazedporcelain.

3. In an apparatus for determining interstitial water content of a wellcore sample by the restored state method, said apparatus having achamber for holding said well core sample, means for supporting asemi-permeable membrane in contact with said well core sample, means forimposing upon said well core sample a pressure of a non-aqueous fluid,and means providing a conduit leading to said semi-permeable membranefor passage of fluid, a semipermeable membrane comprising two unitarydisks of fire clay and a layer of powdered talc positioned between andin contact with said disks of fire clay.

4. In an apparatus for determining interstitial water content of a wellcore sample by the restored state method, said apparatus having achamber for holding said well core sample, means for supporting asemi-permeable membrane in contact with said well core sample, means forimposing upon said well core sample a pressure of a non-aqueous fluid,and means providing a conduit leading to said semi-permeable membranefor passage of fluid, a semi-permeable membrane comprising two unitarydisks of fire clay and a layer of powdered talc of particle size between0.18 and 4.5 microns positioned between and in contact with said disksof fire clay.

FRANK A. ANGONA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 750,235 Tousey Jan. 19, 19041,309,330 Moore July 8, 1919 1,678,676 Lewis July 31, 1928 2,330,721Leverett Sept. 28, 1943 2,365,496 Shaw Dec. 19, 1944 2,400,481 BrabenderMay 21, 1946 2,465,948 Welge Mar. 29, 1949 2,539,355 Reichertz Jan. 23,1951 FOREIGN PATENTS Number Country Date 953 Great Britain 1854

